Systems of the type of this class for tensioning a coil spring are known, for example, from EP 0 115 774 B1 and EP 0 271 782 B1.
The subject of EP 0 115 774 B1 is a spring vice, which has two pressure plates, the distance between which can be changed by means of a tensioning device during the tensioning of a coil spring. These pressure plates have a disk-shaped design and have a circular base each. To tension the coil spring, these two pressure plates with their tensioning surface, which has a pitch, are caused to engage a spring turn each of the coil spring. The spring turns accommodated are located in the end areas of the coil spring axially between the end turns of the coil spring. The tensioning device is subsequently caused to engage the two pressure plates.
The tensioning device comprises here a threaded pipe, which has two diametrically opposite, radially outwardly projecting radial fingers at one of its ends. The corresponding pressure plate has a central opening, through which the threaded pipe with its radial fingers can be passed. Two hollows, which can be caused to be engaged by the radial fingers after a rotation of the threaded pipe by about 90E around the central longitudinal axis of the threaded pipe, are provided in the pressure plate axially on the outside in the edge areas of the opening. The threaded pipe with its radial fingers is thus in pulling connection with the pressure plate via these hollows of the pressure plate, adapted to rotate in unison. Furthermore, the tensioning device comprises a threaded spindle, which has a wrench head, which is in turn provided with a wrench profile designed as a hexagon insert bit. This threaded spindle is mounted in a guide pipe and is supported via a thrust bearing in a head part of the guide pipe, which said head part is located axially opposite the threaded pipe. The guide pipe can be brought into connection with the threaded pipe via elements securing against rotation, adapted to rotate in unison. Positive-locking elements, by means of which the guide pipe can be caused to engage the pressure plate located opposite the threaded pipe, adapted to rotate in unison, are provided at the guide pipe in the area of the head part.
The threaded spindle is screwed into the threaded pipe during the tensioning, so that the guide pipe is pushed over the threaded pipe. The distance between the head part with its two positive-locking elements and the radial fingers of the threaded pipe changes at the same time, so that a coil spring mounted between the two pressure plates is shortened and thus tensioned.
Because of the guide pipe provided and the elements securing against rotation, which project radially to the outside, the tensioning device has a relatively large external diameter here, so that this tensioning device cannot be used for any application on a motor vehicle. Such coil springs of a motor vehicle, which are to be tightened, are seated between an axle body and the body of a motor vehicle. Designs in which the coil spring is accommodated with its end turn on a dome-shaped guide pin are known here for mounting especially at the axle body. The end turn has a relatively small turn diameter, so that the receiving lug also has a relatively small diameter only. The receiving lug is usually provided with a central through hole, whose diameter is likewise relatively small, so that the tensioning device of the prior-art spring vice cannot be passed through the through hole. This means in turn that the diameter of the tensioning device cannot be smaller than a minimum diameter because of the elements securing against rotation, which are provided over the guide pipe. The consequence of this is in turn that the threaded spindle can be used only without a guide pipe and consequently also without the means securing against rotation only in such axle designs with a relatively small through hole, because the threaded spindle itself with its spindle head has such a small diameter that this threaded spindle can be passed through the small through hole of the axle body.
Similarly, the tensioning device in the subject of EP 0 271 782 B1 is provided with a relatively large external diameter. This is due in the subject of EP 0 271 782 B1 to the fact that a guide pipe, which is connected with a coupling pipe, adapted to rotate in unison, is likewise provided here for the threaded pipe. This coupling pipe establishes, in turn, a connection with the threaded pipe, in such a way that they are adapted to rotate in unison, and the guide pipe, the coupling pipe and the threaded pipe can be pushed telescopically into one another. The threaded spindle, which can be screwed into the threaded pipe in this case as well, is likewise mounted in a head part at the outer end of the guide pipe and is supported therein axially via a thrust bearing. This tensioning device can also be used only if the guide pipe and the coupling pipe are omitted, because the threaded spindle with its spindle head can be passed in this case through a relatively narrow through hole of an axle body and can be caused to engage the pressure plate located axially opposite the threaded pipe. However, the consequence of this is that the prior-art spring vice must do without a means securing the two pressure plates against rotation in both cases. However, since this is extremely dangerous for the operating personnel during the operation, such a system for tensioning a coil spring can be used only conditionally.